1. Field of the Invention
This invention relates to fluorinated carbon compositions, and more particularly, to novel fluorinated carbon compositions employed as the conductive components in composite material resistors.
2. Description of the Prior Art
Fluorinated carbon compositions and methods of preparing fluorinated carbon compositions of various stoichiometrics and empirical formulas are well known. Some of the prior art patents relating to fluorinated carbon compositions and methods for making same include, for example, U.S. Pat. Nos. 2,786,874, 3,536,532 and 3,674,432.
Similarly, composite material resistors and methods of making same are well known in the resistor art. Such resistors may be produced, for example, by: mixing a conductive component, e.g., carbon, with a binder and solvent (an inert filler material may also be added to improve the rheology of the fluid composition); applying the fluid composition to any one of a variety of substrates or surfaces by known techniques, such as screen painting or doctor blading; curing and drying the material to remove the solvent; and affixing electrodes to produce a finished resistor.
It has been recognized that it would be desirable to obtain a composite material resistor having a high resistance value and exhibiting certain properties, such properties including temperature stability of resistance over a wide operating temperature range, linear voltage response and minimal Quantech current noise, measured on a Model 315 instrument manufactured by Quan-Tech Laboratories, Inc. Prior art efforts at producing such a high resistance value, composite material resistor with the aforementioned properties, however, involving altering the composition of composite material resistors through varying the relative proportions of conductive component and nonconductive filler material, that is, lowering the conductive component content and proportionately increasing the filler loading, have not produced entirely efficacious results. To obtain a high resistance value resistor by such alteration, large reductions in the amount of conductive component content are required. Such large reductions of the conductive carbon component used in the prior art resistors by dilution with filler give rise to several problems. Difficulties in controlling the resistance value are experienced as slight changes in the content of the conductive component result in large changes in resistance; increased mixing time is required to insure proper dispersion of particles; and, as a practical matter, a lower limit is reached at which further reduction in the content of the conductive component is not practical since at very low levels the resultant Quantech current noise becomes so excessive as to render the resistors commercially unsuitable.
Prior disclosures broadly suggest some of the properties of fluorinated carbon compositions and the efficacy of such properties in other art applications, including the property of fluorinated carbon whereby its resistance may be varied, dependent upon the degree of fluorination, between that of a relatively pure, unfluorinated carbon conductor, and that of an insulator when the carbon is fluorinated to a degree represented by the empirical formula CF.sub.1.12, or above. There is no indication in the prior art, nor is it recognized by those skilled in the art, however, that the carbon conductive component in a composite material resistor may be fluorinated to provide a high resistance value resistor which exhibits the aforesaid desired resistor properties.